Method for projecting image obtained by using liquid crystal panels semiconductor substrate and display apparatus for realizing the same

ABSTRACT

In a projection-type display apparatus using light scattering type liquid crystal devices, light from a light source is reflected by a reflecting mirror through a collecting lens; reflected light is converted by a lens into a parallel light beam, which is injected into liquid crystal devices disposed on three sides through a dichroic mirror, the liquid crystal devices coloring an image in red, green and blue; the image is projected on a screen through again the dichroic mirror, the collecting lens and an enlarging lens. Further a photodetector is disposed at a focal point of the collecting lens and a function of adjusting the position of the light source on the basis of a result of this detection is added.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reproducing apparatus, and inparticular to a projection-type display apparatus for projecting animage to enlarge and display the same.

2. Description of Related Art

Heretofore a projection-type display apparatus for projecting an imageof a small size and enlarging it optically, has been utilized forrealizing a large image having more than 40 inches along a diagonalline. Small size liquid crystal panels are used often as light valvesfor forming a small size original image to be enlarged optically. Thatis, incident light from a light source is intensity-modulated by theliquid crystal panels. Intensity-modulated light thus obtained isprojected on a screen, enlarging it optically by a projection lens, inorder to realize a large image display.

Prior art techniques on such a projection-type display apparatus usingliquid crystal panels are discussed in International Symposium Digest ofSID, pp. 227-230 (1990). Hereinbelow this prior art techniques will beexplained, referring to FIG. 25.

In FIG. 25, this apparatus includes 3 small size transmitting-typeliquid crystal panels 1100, 1101 and 1102 with respective condenserlenses 1112, 1113 and 1114 driven in accordance with image signalscorresponding to color images of red, blue and green, respectively, alight source 1103 of a metal halide lamp, a reflecting mirror 1104, 4dichroic filters 1105, 1106, 1108 and 1109, mirrors 1107 and 1110, and aprojection lens 1111. The optical system except for a screen 1120 iscovered by a cover 1115.

On the other hand, as another prior .art technique, there is known aliquid crystal display apparatus disclosed in JP-A-1-195782. In thisprior art technique a cathode ray tube was used as a light sourceinstead of a discharge tube such as a metal halide lamp. In this priorart, no attention was paid to the life of the light source and thenecessity of maintaining a sufficient amount of light and therefore ithad a problem from a view point of downsizing and maintenance of theapparatus, as explained below.

At first, in this prior art, a light source such as a metal halide lamp,etc. is used. Therefore, although it is possible to generate light witha high brightness, since it emits white light, it is necessary toseparate the white light into different color components by dichroicfilters and to combine color components in order to display it. For thisreason there were problems that the optical system is enlarged andcomplicated so that adjustment of the optical system is difficult andthat mechanism and parts for adjusting the optical axis are required andthereby weight is increased. Also, the life of the metal halide lamp isas short as about 2000 hours. Consequently, supposing that it is used,e.g., 6 hours a day, the life of the lamp expires in about one year. Forthis reason it is inevitable to exchange it during the usable period ofthe optical system and an exchange frequency is as high as about once ayear. Further, the metal halide lamp is expensive and in additionspecial techniques are required for handling and exchange thereof.Therefore, there was a problem that it is difficult for a user to handleor exchange it freely.

Further, the prior art apparatus had a problem that increase in the sizeand complication of the optical system including a position adjustingmechanism and the apparatus are inevitable, because it is necessary toalways use different liquid crystal panels for the 3 primary colors, inorder to obtain a bright color image.

In addition, in the liquid crystal display apparatus using a Braun tube,the problem to be solved is to compensate for slow response of theconventional liquid crystal display apparatus. Also, the Braun tube usedthere was that used in a usual television receiver and therefore therewas a problem that it is difficult to obtain a brighter image, becausesufficient light amount cannot be obtained when the Braun tube is usedas a light source.

Further, in this prior art only one liquid crystal display panel isused. In the projection-type display apparatus, since a small-sizeliquid crystal display panel is used for the light modulation toreproduce a color image, the area of one pixel is extremely small.Therefore, decrease in the aperture ratio is caused, which reduces theefficiency of light utilization. Thus there was a problem that it isdifficult to obtain a brighter image.

There is described a liquid crystal projection-type display apparatususing three TN-(Twisted Nematic-)type liquid crystal panels as an imagesource to obtain a color image by projecting it on a screen in detail inInternational Symposium Digest of SID, pp. 375-378 (1986).

Furthermore, recently, there is described a display apparatus usingpolymer-dispersed-type liquid crystal, in which liquid crystal isdistributed in a transparent resin and by which a state of the liquidcrystal is altered between a scattering state and a transparent state inresponse to a voltage applied from the exterior, instead of the TN-typeliquid crystal, in the literature, International Symposium Digest ofSID, pp. 227-230 (1990) described previously. Still further, in thisarticle, thin film transistors are fabricated by using a polycrystallinesilicon thin film.

Further JP-A-2-12291 can also be cited as a literature, in which theprojection-type display apparatus is described. In this literature, thelight source is located, deviated from the central axis and theprojection lens is disposed at a position symmetric to the light sourcewith respect to the central axis.

Among the above prior art techniques, in which the TN-type liquidcrystal is driven by thin film transistors, there is a problem thatsince the thin film transistors themselves and the parts of wiring andelectrodes for rows and columns cannot transmit light, the area of onepixel electrode effective for the display is decreased and the effectivearea is inevitably reduced usually to about 10% to 30% of the totalarea. Further, because of the light absorption by a polarizing plateinevitable for the TN-type liquid crystal, the light intensity isreduced below 1/2 by the polarizing plate. Therefore, there was aproblem that since the transmittance of the liquid crystal panel isextremely small, a light source consuming high electric power isinevitably used in order to increase the brightness on the screen.

Further, even by those using polymer-dispersed-type liquid crystal,although it is possible to eliminate light loss by the polarizing plate,the area occupied by the thin film transistors and the parts of wiringand electrodes is still great, the transmittance of the liquid crystalpanel is still insufficient.

Furthermore, in a conventional projection-type display apparatus, sincethe light source and the projection lens are located symmetrically withrespect to the central axis, not only it is not possible to reduce thesize satisfactorily, but also an amateur cannot exchange the lamp whenthe lamp serving as the light source is damaged. In the last case he orshe should send the display apparatus to the maker so as to exchange thedamaged lamp. This is because the resolution is extremely lowered, if adeviation of the optical axis, which is as small as several micrometers,is caused on the exchange of the light source.

SUMMARY OF THE INVENTION

The present invention has been done in view of the situation describedabove and the object thereof is to provide a method for enlarging andprojecting an image, by use of liquid crystal panels and aprojection-type display apparatus having a small size and a highprecision for realizing the method.

In order to achieve the above object, a projection-type displayapparatus according to the present invention includes a control section,an optical signal generating section including a plurality of liquidcrystal panels, a combining optical system and a projecting section. Thecontrol section inputs an electric image signal representing an imageand generates a plurality of electric signals. The plurality of electricsignals thus generated are supplied to the plurality of liquid crystalpanels in the optical-signal generating section. A plurality of opticalsignals are generated by using the plurality of liquid crystal panelsand supplied to the combining optical system. The combining opticalsystem generates an optical image signal by combining the plurality ofoptical signals. The optical image signal is projected on a screen bythe projecting section.

According to the present invention, the efficiency of light utilizationof the liquid crystal panel can be almost doubled by using alight-scattering-type liquid crystal panel requiring no polarizing plateand further the effective display area can be increased by using areflection-type liquid crystal panel. In this way it is possible torealize a bright projection-type display apparatus with a low electricpower consumption. Further, the size of the optical system can bereduced by using a reflective-type projection optical system.Furthermore, since peripheral driving circuits and various kinds ofcontrol circuits can be integrated in the liquid crystal panel, in whichactive elements such as transistors are formed on a silicon monocrystalwafer. Therefore, increase in the reliability owing to decrease in thenumber of connecting terminals, simplification in the mounting, and downsizing are possible. Still further, the apparatus is so constructed thatlight intensity and light amount can be measured more easily bydetecting a light focusing point within the display apparatus and thatthe optical axis deviated on exchange of the lamp, vibration, etc. canbe readjusted easily. Therefore, even an amateur can carry out lampexchange, etc., resulting in improvement of usability of the apparatus.

In addition, according to the present invention, a plurality ofmonochromatic cathode ray tubes having different greatest intensitywavelength regions such as red (R), green (G) and blue (B), which arethree primary colors of light, are used as the light source and hencethe life of the apparatus is longer than 10000 hours. Thus, it ispossible to provide a projection-type color display apparatus having noproblem in maintenance of the light source and a sufficiently highutility. Further, even at the end of the life a CRT is never misfired,as a lamp is. Thus, according to the present invention, it is possibleto provide easily a projection-type color display apparatus, whoseduration of usability is remarkably longer. Furthermore the CRT can emitlight of different colors of RGB separately at a high efficiency byselecting suitably fluorescent material. Consequently, according to thepresent invention, it is possible to obtain easily a display apparatushaving excellent color reproduction characteristics.

In general, in a case of using a CRT for image display so as to increasebrightness on the screen, it is necessary to increase current intensityof the electron beam. However, when the current intensity is increased,the diameter of the electron beam is increased, which causes lowering inthe resolution of a projected image. That is, in a usual CRT, thebrightness on the screen and the resolution are in a trade-off relation.Thus, in the case where the CRT is used as a light source for aprojection-type display apparatus, the resolution is determined by theliquid crystal panel and therefore, even if the diameter of the electronbeam is increased. This doesn't cause lowering in the resolution.Consequently according to the present invention, it is possible toincrease satisfactorily the current intensity of the electron beam andin this way to realize easily a projection-type display apparatus havinga high brightness and a high resolution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an optical system of a liquid crystalprojection-type display apparatus relating to a first embodiment of thepresent invention;

FIG. 2 is an equivalent circuit diagram representing one element, i.e.,a pixel in a liquid crystal panel used in the display apparatusaccording to the present invention;

FIG. 3 is a cross-sectional view showing the construction of the liquidcrystal panel shown in FIG. 2;

FIG. 4A is a block diagram of a circuit integrated in the liquid crystalpanel shown in FIG. 2;

FIG. 4B is a diagram representing the construction of the circuit shownin FIG. 4A in detail;

FIG. 4C is a diagram representing a circuit 72 shown in FIG. 4B indetail;

FIG. 4D shows timing charts for explanation of an operation of theliquid crystal panel;

FIGS. 5A and 5B are diagrams for explaining the operation of the liquidcrystal panel shown in FIG. 2;

FIGS. 6A and 6B are diagrams for explaining the operation of anotherliquid crystal panel used for realizing the present invention;

FIGS. 7A and 7B are diagrams for explaining the operation of stillanother liquid crystal panel used for realizing the present invention;

FIG. 8A is a diagram showing a modified example of the equivalentcircuit shown in FIG. 2;

FIG. 8B is a diagram showing another modified example of the equivalentcircuit shown in FIG. 2;

FIG. 9 is a block diagram showing a modified example of the integratedcircuit shown in FIG. 4A;

FIG. 10 is a cross-sectional view of a modified example of the liquidcrystal panel shown in FIG. 3;

FIGS. 11A and 11B are schematical diagrams showing a state when a liquidcrystal panel is mounted on the dichroic prism shown in FIG. 1;

FIG. 12 is a diagram showing an optical system of a projection-typedisplay apparatus, in which a half mirror is used instead of thereflecting mirror in the display apparatus shown in FIG. 1;

FIG. 13A is a diagram showing the construction of a second modifiedexample of the present invention;

FIG. 13B is a diagram representing a method for dividing a liquidcrystal panel into a panel for odd scan lines and a panel for even scanlines in the modified example shown in FIG. 13A.

FIGS. 13C and 13D are diagrams showing circuit patterns corresponding topixels in the panels for odd and even scan lines, respectively;

FIG. 14 is a diagram showing the construction of a projection-typedisplay apparatus having a lamp position adjusting function according tothe present invention;

FIG. 15 is a block diagram showing a projection-type display apparatusaccording to a second embodiment of the present invention;

FIGS. 16A and 16B are diagrams for explaining the operation of adispersed-type liquid crystal panel in the second embodiment of thepresent invention;

FIGS. 17A and 17B are diagrams for explaining the construction andcharacteristics of an interference film, respectively, used in thesecond embodiment of the present invention;

FIG. 18 is a block diagram showing a control system shown in FIG. 15;

FIGS. 19A to 19D are diagrams for explaining the operation of the secondembodiment of the present invention;

FIG. 20 is a block diagram showing a modified example of theprojection-type display apparatus according to the present invention;

FIG. 21 is a block diagram showing the control system in the modifiedexample;

FIGS. 22A to 22D are diagrams for explaining the operation of the liquidcrystal panels, CRT (R), CRT (G) and CRT (B), respectively, in themodified example;

FIGS. 23A to 23E are timing charts for explaining FIGS. 22A to 22D,respectively;

FIG. 24 is a diagram showing a modified example of the construction ofthe tube surface of the cathode ray tube in the second embodiment of thepresent invention; and

FIG. 25 is a diagram showing the construction of a prior art example ofthe projection-type display apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow the projection-type display apparatus according to thepresent invention will be explained in detail, referring to the attacheddrawings.

FIG. 1 represents an optical system of the display apparatus accordingto the present invention, which includes a lens 13 for focusing whitelight emitted from a light source 11 on a reflecting mirror 12, a lens16 for transforming the white light reflected by the reflecting mirror12 into parallel light and irradiating the parallel light to areflecting-type of liquid crystal panels 15-R, 15-G and 15-Bcorresponding to the three primary colors through a separating/combiningoptical system 14, and a lens 17 for projecting on a screen light whichhas been reflected by the liquid crystal panels 15-R, 15-G and 15-B andpassed again through the optical system 14 and the lens 16. The threeliquid crystal panels are driven by a driving circuit 18, in response toimage signal V_(S) (R), V_(S) (G) and V_(S) (B), respectively obtainedby separating a color image signal V_(S) into the three primary colorcomponent signals.

A metal halide lamp with a reflecting mirror 11a is used as the lightsource 11 and a dichroic reflecting mirror 11a is used for reflectingonly visible light so that infrared light unnecessary for the display isnot directed to the liquid crystal panels. The lens 13 plays the role offocusing light on the reflecting mirror 12 and is located so that thedistance from the principal point of the lens to the light focusingportion of the reflecting mirror 12 approximately corresponds to thefocal length. Since the light focusing portion of the reflecting mirror12 is located at a point deviated from the optical center line of thelenses 16 and 17, the light focusing portion of light after having beenreflected by the liquid crystal panels 15-R, 15-G and 15-G is located ata point deviated from the reflecting mirror 12. Therefore, there is noloss of the reflected light by the reflecting mirror 12. The reflectingmirror 12 is provided at 45 degrees with respect to the center line oroptical axis of the lens 16. Incident light to the mirror 12 has anincident angle of more than 45 degrees and the incident angle ispreferably within a region from 45 to 55 degrees. The lens 16 is locatedat a point distant from the light focusing point on the reflectingmirror 12 approximately by its focal length so that incident light tothe lens 16 is transformed into parallel light, which is irradiated inthe succeeding optical system 14. The optical system 14 is composed of adichroic prism, which reflects the red component of the incident whitelight rightward in the figure and the blue component leftward, andtransmits the green component downward.

The liquid crystal panels 15-R, 15-G and 15-B are of reflection-typeusing light-scattering type liquid crystal and they are driven inresponse to the different primary color component signals obtained byseparating the image signal. If a transparent portion on each panel isbright on the screen, the light scattering portion is displayed to bedark on the screen. In the equivalent circuit of each of pixels in eachof the liquid crystal panels 15-R, 15-G and 15-B, as shown in FIG. 2,the gate of a transistor is connected to a row electrode 47, the drainto a column electrode 46 and the source to a pixel electrode. Further,in FIG. 2, there is disposed a storage capacitor 52 in parallel with acapacitor of a pixel 50 of liquid crystal which is connected to atransparent pixel electrode 51 common to all the pixels. The other endof the storage capacitor 52 is connected to an electrode 53 exclusivelyused therefor to hold the storage capacitors for all the pixels at asame potential. This storage capacitor 52 is disposed for the purpose ofpreventing that the driving current of the liquid crystal is lowered inaccordance with its proper leak current and therefore it is unnecessary,if the liquid crystal has a sufficiently high impedance.

FIG. 3 is a cross-sectional view of the liquid crystal panel. Alight-scattering type of liquid crystal 61 is put between two substrates60 and 62. The lower substrate 60 is a single crystal wafer of silicon.On the wafer, transistors 63 are formed. The source electrode of eachtransistor is connected to a pixel electrode 64. This pixel electrode ismade of metal such as aluminum, etc., which serves as a light reflectinglayer. The substrate 62 opposite to the substrate 60 is made oftransparent material such as glass, policarbonate, acrylate resin or thelike, on the inner surface of which a transparent electrode 65 isdisposed. Reflection by the transparent electrode 65 is prevented bycontrolling a thickness or the like of the electrode 65. Further, inorder to prevent worsening in the image quality due to reflection on thesurface, there is disposed a reflection preventing layer 66 withmultiple layers of dielectric substance on the outer surface of thesubstrate 62 or a silicon gel layer having substantially the samerefractive index between the dichroic prism 14 and it.

FIG. 4A is a diagram showing the construction of the circuit integratedin the wafer, in which there are circuits 71, 72 and 73 for driving adisplay section 70 including pixels arranged in a matrix manner.Reference numeral 71 denotes a scanning side driving circuit fortime-sequentially giving a gating voltage pulse to a group of rowelectrodes each connecting gates of the transistors, 72 a signal sidedriving circuit for time-sequentially giving a group of columnelectrodes a image signal, and 73 a control circuit for controlling boththe driving circuits 71 and 72.

Next a detailed construction of a liquid crystal light valve includingthe circuits 71, 72 and 73 and the operation thereof will be explained.

FIG. 4B shows the circuit construction of the light valve. The lightvalve includes a liquid crystal display section 70, a horizontalscanning circuit 72-1, a sample circuit 72-2, a vertical scanningcircuit 71-1 and an AND circuit group 71-2. Each of the pixels of theliquid crystal display section 70 includes a transistor 70a, a storagecapacitor 70b and the liquid crystal capacitor 70c. The pixels arearranged in a matrix form of m rows and n columns to construct theliquid crystal display section. The horizontal and vertical scanningcircuits 71-1 and 72-1, the sample circuit 72-2, and the AND circuitgroup 71-2 are for sequentially driving the display section 70 in unitsof pixels. These driving circuits are disposed on the monocrystalsilicon constituting the display section 70.

The circuit 72-1 inputs a start signal STA and a clock signal CLK from acircuit 73 and outputs sample signals. PH1 to PHn. A switching circuitas the sample circuit 72-2 supplies alternated video signals VI1 and VI2as drain signals Vd1 to Vdn to drains of the transistors in the displaysection 70 in synchronism with the sample signals PH1 to PHn. Thecircuit 71-1 inputs a start signal FST and a clock signal CKV andoutputs vertical scanning signals PV1 to PVm. The AND circuit group 71-2outputs gate signals VG1 to VGm in accordance with a control signal CNTand the signals PV1 to PVm to control scanning timing for the column orgate lines.

Next, the horizontal and vertical scanning circuits will be described indetail, referring to FIG. 4C. Each of these circuits includes D typeflip-flops FF₁ to FF_(p), inverters INV1 to INVp and level convertingcircuits LS1 to LSp. The p is n for the horizontal scanning circuit andm for the vertical scanning circuit. The flip-flops are connected inseries to construct a shift register. A low voltage O-VDD (+5 V) issupplied to the flip-flops FF and the inverters INV and a high voltageVSS(-15 V)-VDD(+5 V) is supplied to the level converting circuit LS.

Next, the operation of the liquid crystal light valve will be explainedwith reference to timing charts shown in FIG. 4D. The start signal STAfor the horizontal scanning circuit has, as a period, one horizontalscanning period. The sample signals PH1 to PHn are generated by catchingthe start signal STA at the rising timing of the clock signal CLK and bysequentially shifting the caught signal in the shift register, using theclock signal CLK.

The start signal FST for the vertical scanning circuit has, as a period,a one-frame scanning period. The vertical scanning signals PV1 to PVmare generated by catching the start signal FST at the rising timing ofthe clock signal CKV and by sequentially shifting the caught signal inthe shift register in synchronism with the signal CKV, similarly to thehorizontal scanning circuit.

The video signals VI1 and VI2 have a central voltage equal to areference potential of the liquid crystal pixels 70b, the polaritiesthereof are opposite to each other and inverted for every horizontalscanning. These video signals are sampled at the timing of the samplesignals from the horizontal scanning circuit and electric chargecorresponding to the sampled signal is stored in the storage capacitor70c.

In the present invention, polymer-dispersed-type liquid crystal is usedas the light-scattering-type liquid crystal and the operationalcharacteristic thereof will be explained, referring to FIGS. 5A and 5B.The polymer-dispersed-type liquid crystal panel includes a liquidcrystal layer so constructed that nematic liquid crystal 82 is containedin an encapsulated manner in transparent organic material 81, e.g.,polyvinyl alcohol. When no voltage is applied to a liquid crystal panel,nematic liquid crystal molecules are oriented parallel to the wall ofthe capsule, as shown in FIG. 5A. Since the liquid crystal moleculeshave an approximately elliptic cross-sectional construction, there arethe liquid crystal molecules each having a minor or short axis of theellipse with respect to incident light in a vertical direction from anup side to a down side of the figure with a high probability. On theother hand, when a voltage is applied thereto from a driving voltagesource 83, since the liquid crystal molecules are oriented so that themajor or long axis thereof is directed in the direction of an electricfield due to the applied voltage, as shown in FIG. 5B, the incidentlight comes into the liquid crystal molecules in the major axisdirection thereof and thus is transmitted. Therefore, in apolymer-dispersed-type liquid crystal selected so that the refractiveindex of the organic material 81 and that of the liquid crystalmolecules only in the major axis direction are approximately equal toeach other, when no voltage is applied thereto, since the refractiveindices of the organic material and the liquid crystal are differentfrom each other at the surface of the capsules, the incident light isscattered. On the contrary, when a voltage is applied thereto, since therefractive indices of the organic material and the liquid crystal areapproximately equal to each other, no scattering of the incident lighttakes place and hence a liquid crystal layer is transparent.

In a liquid crystal panel having the construction, using suchpolymer-dispersed-type liquid crystal, as shown in FIG. 4A, a part ofthe liquid crystal layer is transparent for pixels, under an electricfield of sufficient intensity operated by transistors. Incident light tothe liquid crystal panel in a downward direction passes through theliquid crystal layer and is reflected almost completely (in practiceabout 80 to 90%) by the reflecting layer serving as the pixel electrode.As a result, a part of an image corresponding to those pixels aredisplayed to be bright on the screen. On the contrary, when no electricfield operates to pixels, the incident light is scattered stronglywithin the liquid crystal layer, so that scattered light doesn't reachthe screen, resulting in dark display of a part of the imagecorresponding to the pixels. Further, since the degree of the scatteringvaries gradually with increasing the voltage associated with theelectric field, intermediate tone display can be made through voltagemodulation.

In the first embodiment described above, the polarizing plate, which wasinevitable for the TN-type liquid crystal, can be omitted by using thelight-scattering-type liquid crystal, and the brightness can beapproximately double compared to the case of the TN-type liquid crystal.Also, by using the reflecting-type of liquid crystal panels, the pixelelectrodes can be disposed on the transistors and the wiring electrodes,resulting in increasing the efficiency of light utilization.Consequently it is possible to realize a bright display with a lamp of alow electric power consumption, compared to a conventionalprojection-type display apparatus.

Further, by using the reflection-type projection optical system, thecolor-separating optical system and the color-combining optical systemcan be used in common, resulting in down sizing being possible.

Furthermore, owing to the fact that the peripheral driving circuit isintegrated on the silicon monocrystal wafer, the number of connectingpoints with the exterior can be significantly reduced and remarkableeffects can be obtained on improvement of the reliability andsimplification of mounting, thereby resulting in the down sizing of theapparatus.

Next, a first modified example of the liquid crystal panel will beexplained, referring to FIGS. 6A and 6B. In this modified example, thelight-scattering-type liquid crystal is similar to that described in thefirst embodiment in that nematic liquid crystal 92 is enclosed byorganic material 91. However, the nematic liquid crystal is notencapsulated (in an approximately spherical shape), but filled in gapsof the organic material, as shown in FIG. 6A. Although an opticalbehavior of the liquid crystal under the presence or absence of theelectric field is identical to that described in the first embodiment,as apparent from FIGS. 6A and 6B, since many parts of the liquid crystalconnect to both the electrodes in the direction of electric field, thedriving voltage can be lower than that required for the encapsulatedpolymer-dispersed-type liquid crystal.

Now a second modified example of the liquid crystal panel will beexplained, referring to FIGS. 7A and 7B. A liquid crystal materialtaking the smectic A phase is used as the light-scattering-type liquidcrystal. When no electric field operates thereto, the smectic A phaseliquid crystal takes an orientation state called a focal conic structurein which light is scattered. On the other hand, when electric fieldoperates thereto, the liquid crystal takes a homeotropic structure 102,in which the major axes of molecules of the liquid crystal are arrangedproperly in the direction of the electric field and thus the liquidcrystal is in a transparent state. In this way the same display asdescribed above can be achieved. In this modified example, only liquidcrystal material is sealed between the electrodes and the panel can befabricated by a method almost identical to that used for a conventionalapparatus using TN-type liquid crystal.

Next, a third modified example of the liquid crystal panel will beexplained, referring to FIG. 8A. In this modified example a switchingcircuit 111 for selecting and outputting the of two inputs is provided,for every pixel and formed of a plurality of transistors of each of thepixels. This switching circuit 111 reads out display informationinputted from the column electrode 113 in response to a pulse voltagesignal from the row electrode 112 and selects either one of the displayvoltages V(on) or V(off) to drive a pixel 114 of the liquid crystal.Further, if the circuit is constructed so as to hold the displayinformation once read out, until the succeeding pulse voltage arrives,since V(on) or V(off) is always applied to the pixel 114 of the liquidcrystal panel, there is no period of time when the circuit is in anopened state which is peculiar to the conventional example, viewed fromthe liquid crystal panel, and impedance control for the liquid crystalpanel can be alleviated. Further, an effect of making the storagecapacitor 115 unnecessary can be obtained. Although, in the presentmodified example, only two-valued display is possible, because aswitching circuit having two inputs and one output is used, it isapparent that extension to multi-valued display can be made byincreasing the number of inputs of the switching circuit and byincreasing the display information and the number of display voltages incorrespondence with the increase of inputs.

Next, a fourth modified example of the liquid crystal panel will beexplained, referring to FIG. 8B. In this modified example, each of thepixels has a sample hold circuit S/H and an analogue amplifier Amp. Thecircuit S/H reads out analogue image information from the columnelectrode 122 in response to a pulse voltage from the row electrode 121to hold the same. The analogue amplifier Amp is in charge of amplifyingthis analogue image information up to a predetermined level to drive aliquid crystal pixel. The liquid crystal pixel 123 is always driven by avoltage source of low impedance similarly to the third modified exampleand therefore it is possible to alleviate the impedance control for theliquid crystal panel and further to make the storage capacitor 124unnecessary.

Next, a fifth modified example of the liquid crystal panel will beexplained, referring to FIG. 9. In this modified example, not only thedisplay driving section 131 and the peripheral circuit 132 but also acontrol circuit including a frame memory 133 for storing displayinformation for one screen and a controller for the frame memory areintegrated in the silicon monocrystal wafer. By adopting such aconstruction, an external apparatus, e.g., personal computer is requiredonly, to write display information in the frame memory 133 and is notrequired to generate control timing signals and to perform high speedtransfer of the display information in a time sequence manner.

FIGS. 11A and 11B show an example of the method for mounting the liquidcrystal panel in the present embodiment. In the example, wiringterminals to the exterior are disposed previously on the dichroic prism141 serving as the color separating/combining optical system andelectric connection with the silicon monocrystal wafer 142 is effectedthrough solder bumps or a silver paste or the like which is obtained bydispersing conductive particles into a material having adhesiveproperty, as shown in FIG. 11B, i.e., on the basis of the chip-on-glassmethod. It is a matter of course that a liquid crystal layer 143 islocated between the prism 141 and the wafer 142, that an oppositeelectrode 144 is disposed either on the liquid crystal or on thetransparent glass and that connection from the prism 141 to the externalcircuit through the solder bumps is effected by means of a flexible flatcable 145. By adopting such a mounting method, packaging of the liquidcrystal panel can be simplified and hence down sizing of the apparatuscan be intended.

Next, a sixth modified example of the liquid crystal panel willexplained, referring to FIG. 10. In this modified example, a glasssubstrate 151 of the liquid crystal panel on the incident light side isinclined with respect to the optical axis. In this way, light componentswhich are reflected by the surface of the glass substrate 151 and whichwould originally lowers the display quality, are deviated from theoptical axis so that they cannot arrive at the screen. Thereforeworsening of the display quality can be prevented. Also, light passingthrough the liquid crystal layer 152 in the transparent state andreflected by the surface of the silicon monocrystal wafer propagatesalong the predetermined optical axis and hence the display operation isnot hindered.

Next, a first modified example of the first embodiment of the presentinvention will be explained referring to FIG. 12. In this modifiedexample, a half mirror 161 is used instead of the reflecting mirror,white light emitted from a light source 162 is transformed toapproximately parallel light by a lens 163. Approximately 50% of thisparallel light is reflected by the half mirror 161 to the left of thefigure and income to a dichroic prism 164 serving as the colorseparating/combining optical system. The operations of the dichroicprism and liquid crystal panels 165-R, 165-G and 165-B are identical tothose described in the first embodiment. Light components reflected bythe liquid crystal panels are combined and income again in the halfmirror 161. Thus, approximately 50% of the incident light to the halfmirror 161 is projected on a screen by a projection lens 166. Althoughthe present optical system has an optical loss, the optical system canbe simplified and a remarkable effect of down sizing of the apparatusand lowering in the price can be obtained.

Next, a second modified example of the first embodiment of the presentinvention will be explained. In general, in the case where transistors,etc. are formed on a silicon wafer, flatness of the surface of the waferis worsened. For this reason, even if the pixel electrode is made ofaluminium having a high reflectivity, light is scattered on the surfaceof the electrode and therefore effective light amount projected on thescreen through the projection lens is reduced. In the present modifiedexample, in order to prevent lowering in the efficiency of lightutilization due to unevenness of the surface of the pixel electrode asdescribed above, the scan lines of the screen are divided into odd scanlines and even scan lines and separate liquid crystal panels are usedtherefor.

A dividing state of the scan lines of the screen will be explained,referring to FIG. 13B. FIGS. 13C and 13D are a diagrams showing theconstructions of the pixels on the panels for odd and even scan linesobtained by the division, respectively. The screen 171 is so constructedthat a number of pixels 172 are arranged in a two-dimensional matrixform. The screen 171 has scan lines from Line No. 1 to 2N. Here the scanlines are divided into two groups of the odd scan lines and the evenscan lines. That is, the panel for odd scan line is constructed by onlythe pixels on the odd number scan lines among the pixels constitutingthe screen 171. In FIG. 13B, on the panel for odd scan line, the scanline numbers are 1, 3, 5, --, 2N-1. On the contrary, the panel for evenscan lines is constructed by only the pixels on the even number scanlines. In FIG. 13B, on the panel for even scan lines, the scan linenumbers are 1 2, 4, --, 2N. Each of the pixels on the liquid crystalpanels obtained by division occupies an area twice as large as the areaoccupied before the division. In each of the panels for odd and evenscan lines, circuit elements such as transistors, etc. are formed on theportion where a pixel is removed by the division.

The positional relation between the pixels and the transistors will beexplained, referring to FIGS. 13C and 13D. In FIG. 13C, a transistorportion 175 is formed at the intersection of a scan line electrodewiring 173 and a signal electrode wiring 174. Further a pixel electrode176 made of a material or the like having high reflectivity such asaluminum is disposed so as to cover a pattern of the transistor portion175 and parts of the patterns of the scan line electrode 173 and thesignal electrode 174 (in the figures this situation is shown in aclairvoyant state so that the positional relation of the transistorportion 175, etc. is clearly seen). In the panel for odd scan lines, aflat portion 177 of the pixel electrode corresponds to each pixel oneach of the odd scan lines of the screen before the division (upper halfin the figure) and the transistor portion 175 or the like is arranged ina part corresponding to pixels on each of the even scan lines before thedivision. In FIG. 13D, a transistor portion 180 is formed at theintersection of a scan line electrode wiring 178 and a signal electrodewiring 179. The transistor portion 180 and a flat portion 182 for eachpixel in the even scan lines are arranged in reverse to the case in theodd scan lines.

As described above, the flat portion can always be obtained in therespective pixel electrode portions by dividing the scan lines of thescreen into the odd and even scan lines and the area thereof isapproximately equal to that of the each pixel of the screen before thedivision. For this reason light can be satisfactorily reflected and thusit is possible to realize a liquid crystal projector having a highefficiency of light utilization.

A display apparatus capable of projecting a color image on a screen,using the two panels for odd and even scan lines will be explained,referring to FIG. 13A. The fundamental construction of this displayapparatus is identical to that of the display apparatus shown in FIG.12. Therefore the identical constituent parts are indicated by samereference numerals and explanation thereof will be omitted.

In this display apparatus, in addition to the display apparatus shown inFIG. 12, liquid crystal panels 165-B', 165-G' and 165-R' and a dichroicprism 164' are disposed on the transmission side of the half mirror 161.The arrangement of the liquid crystal panels 165-B', 165-G' and 165-R'and the dichroic prism 164' is identical to that of the displayapparatus shown in FIG. 12. However, an image obtained from the liquidcrystal panels 165-B' is inversed in the left and right sides, comparedto that obtained from the liquid crystal panel 165-B. This can beachieved by scanning horizontally the liquid crystal panel 165-B' fromthe right side to the left side, when the liquid crystal panel 165-B isscanned horizontally from the left side to the right side.

About a half of the light emitted from the light source 162 is reflectedby the half mirror 161 and income into the dichroic prism 164, while theremaining half passes through the half mirror 161 and is income into thedichroic prism 164'. An odd scan line image and an even scan line imageare outputted from the dichroic prisms 164 and 164', respectively, onthe basis of the incident light to the prisms 164 and 164'. The odd scanline image passes through the half mirror 161, while the even scan lineimage is reflected by the half mirror 161. In this way an image for allthe scan lines is produced on the projection lens 166 side after thehalf mirror 161.

As apparent from the above description, contrarily to the fact that inthe display apparatus shown in FIG. 12 only 50%×50%=25% of the lightemitted from the light source 162 is utilized it is possible to utilizethe light with a higher efficiency, i.e., the efficiency of 50% by usingthis display apparatus.

Although, in this example, a half mirror is used, it is possible to usea beam splitter instead thereof. Since this can be done easily by aperson skilled in the art, explanation thereof will be omitted. Furtherit is also possible to dispose two display apparatuses shown in FIG. 12for the odd scan line image and the even scan line image, respectively,and to combine those image on a screen so as to provide a color image.

Next, a second modified example of the first embodiment of the presentinvention will be explained, referring to FIG. 14. FIG. 14 shows aprojection-type liquid crystal display apparatus, in which a section forrealizing a lamp position adjusting function is integrated. In thisfigure the constituent parts identical to those shown in FIG. 1 areshown by same reference numerals.

In the present example, the lamp position adjustment in exchanging thelamp 11 serving as a light source is effected automatically.

Since it is thought that the lamp 11 is the exchange part having theshortest life in the present optical system, the exchange thereof isinevitable. Since this exchange is accompanied by usually complicatedposition adjusting work it was necessary that it is effected by aspecialist. However, the present modified example is provided with aposition fine-adjusting mechanism 1702 for adjusting finely the positionof the lamp, a driving circuit 1703 for driving the mechanism 1702, alight detecting section 1704, a light detecting section moving mechanism1705 and a light detecting section driving circuit 1706.

Now, the operation thereof will be explained. In the present opticalsystem a light focusing point is located at a point P within the opticalsystem. It is sufficient to adjust the position of the lamp inexchanging it so that the light focusing point is positioned accuratelyat this point P. For this reason, the system is so constructed that thelight detecting section 1704 can be positioned at the point P.Consequently the moving mechanism, which moves the light detectingsection 1704 located usually at a position where the section 1704doesn't obstruct the optical path, to the point P in exchanging thelamp, and the driving circuit 1706 therefor are driven. The section 1704includes a light detecting element smaller than the light focusing spotat the point P. When the light amount detected by this light detectingelement is highest, this means that light is focused just at this pointP. At this time a light detection output is sent to the driving circuit1703 for driving the adjusting mechanism 1702 to adjust finely theposition of the lamp.

Since it is usually difficult to discern the greatest light amount, itis possible also to store in advance the optimum light amount region,depending on the used lamp 11 and to terminate the adjustment, when thedetected light amount is in the light amount region described above.Further it is also possible to display the output of the photodetectorand the optimum light amount region and to construct the adjustingmechanism so as to be driven manually so that even an amateur can effecteasily the fine adjustment according to the display. In this way, whenthe light detecting section 1704 is returned to its original positionafter having adjusted automatically or manually the position of thelamp, where the section 1704 doesn't obstruct the optical path so thatthe system can perform the function as a display apparatus. Further,since displacement of the photodetector is determined unambiguously, ifthe optical system is determined, it can be moved manually. The presentphotodetector can also be used for adjusting the optical axis, etc. Theadjusting mechanism 1702 capable of being moved one-, two- orthree-dimensionally can be used. Furthermore, although, in the presentmodified example, a reflecting-type liquid crystal display apparatus hasbeen described, it is a matter of course that in a transmitting-typeliquid crystal display apparatus. The lamp position adjustingphotodetector according to the present invention can also be used, ifthe light focusing point is disposed within the apparatus, so that lampexchange or readjustment of a misaligned optical axis can be easilyeffected. Although, in the modified example described above, the lightamount to be detected by the photodetector is supposed, light intensityor the like may be measured. Since lamp exchange can be effected easilyaccording to the modified example described above, it is suitable foruse at a place, where there is no specialist, such as domestic use.

Hereinbelow a projection-type display apparatus according to a secondembodiment of the present invention will be explained in detail,referring to the attached drawings.

FIG. 15 shows the second embodiment of the present invention and theprojection-type display apparatus according to the present embodiment iscomposed of three liquid crystal light valves 201, 204, 207, three CRTs202, 205, 208 acting as plane light sources, a dichroic prism 210, aprojection lens 211, and a control system 213. It includes further ascreen 212 as an attached installation.

The liquid crystal light valves 201, 204 and 207 for red, green and blueare controlled in accordance with image signals for red, green and blueimages, which are supplied by the control system 213, tointensity-modulated red light 203, green light 206 and blue light 209emitted by the fluorescent surfaces of the CRTs 202, 205 and 208 forred, green and blue which are disposed sufficiently closely to theliquid crystal light valves 201, 204 and 207, in order to generate red,green and blue images, respectively.

The red light 203 and the blue light 209 thus intensity-modulated arereflected by interference films 210a and 210b of the dichroic prism 210and income into a projection lens 211. The intensity-modulated greenlight 206 passes through the dichroic prism 210 and is income into theprojection lens 211. As the result, three-colored light of the red light203, the green light 206 and the blue light 209 is combined orsynthesized and projected to the screen 212 by the projection lens 211so that a color image is displayed on the screen 212.

The liquid crystal light valves 201, 204 and 207 and the CRTs 202, 205and 208 are arranged sufficiently closely to each other, respectively.However, in order that lights emitted by the different CRTs 202, 205 and208 are income into the projection lens 211 with a further higherefficiency, the interference film 301 for red is attached to the tubesurface of the CRT 202 for red; the interference film 302 for green isattached to the tube surface of the CRT 205 for green; and theinterference film 303 for blue is attached to the tube surface of theCRT 208 for blue.

Consequently, according to the present embodiment the efficiency of thelight utilization is high and it is possible to reproduce easily asufficiently bright color image.

In the present embodiment, dispersed-type liquid crystal light valves inwhich thin film transistors (TFT) are incorporated, are used for theliquid crystal light valves 201, 204 and 207 modulating the differentcolors. Therefore the construction and the principle of thedispersed-type liquid crystal light valve will be explained, referringto FIGS. 16A and 16B.

As shown in FIG. 16A, a dispersed-type liquid crystal light valve is soconstructed that a liquid crystal layer 223 including a number of liquidcrystal grains 223a is sandwiched between a transparent substrate 220ahaving a transparent electrode 221a and that a transparent substrate220b having similarly a transparent electrode 221b, which is opposite tothe former, and a signal source 224 and a switch 225 are connectedbetween these transparent electrodes 221a and 221b. Since the manyliquid crystal grains 223a are oriented at random, when the switch 225is turned-off so that no electric field is generated in the liquidcrystal layer 223, light income into the liquid crystal layer 223 atthis time is scattered, as shown in the figure and therefore the liquidcrystal light valve holds its opaque state. 0n the contrary, when theswitch 225 is turned-on and the electric field by the signal source isgenerated in the liquid crystal layer 223 between the transparentelectrodes and when the voltage corresponding to this electric fieldexceeds a certain voltage V₁, all the liquid crystal molecules in eachof the liquid crystal grains within the liquid crystal layer 223 arealigned in the direction of the electric field. In this way the incidentlight passes therethrough and thus the liquid crystal light valvebecomes transparent. That is, this dispersed-type liquid crystal lightvalve is switched-over between the opaque state and the transparentstate, depending on the presence or absence of the signal voltage, andthus performs a light valve function. Further, when the applied voltageis controlled at values lower than V₁, the degree of the scattering canbe controlled. As the result, the light valve can also displayintermediate tones by using a voltage signal modulated by the imagesignal as the signal source 224 and thus act as an image reproducingdevice.

Since this dispersed-type liquid crystal light valve requires nopolarizing plate, it has a high efficiency of light utilization.Further, in the present embodiment as described previously, aninterference film for red 301 is stuck or laminated on the tube surfaceof the CRT for red 202; an interference film for green 302 is stuck onthe tube surface of the CRT for green 205; and an interference film forblue 303 is stuck on the tube surface of the CRT for blue 208. As theresult, a collimator lens effect is given to the front glass part ofeach of the CRT. Therefore, no generated light is uselessly dispersed,which increases remarkably the efficiency.

Next the operation of the interference film stuck on the tube surface ofeach of the CRTs will be explained, referring to FIGS. 17A and 17B. Asshown in FIG. 17A, a fluorescent plane 231 is disposed on the innersurface of the face plate (light emitting plate) 230 of the CRT and theinterference film 232 is stuck on the surface opposite to thefluorescent plane 231, when the fluorescent plane 231 is irradiated withan electron beam 233, the fluorescent plane 231 emits fluorescence atspecified wavelengths. In the case of the CRT for red, light is emittedprincipally in a red wavelength region and in the case of the CRT forgreen, light is emitted principally in a green wavelength region.Further, in the case of the CRT for blue, light is emitted principallyin a blue wavelength region. This light is emitted by each of thefluorescent planes 231 over a wide angular region. The interference film232 is composed of a multi-layered evaporation film of a dielectricsubstance having a refractive index different from that of glassmaterial constituting the face plate 230 and it can have an incidentangle dependency concerning its transmission characteristics for lighthaving a predetermined wavelength. For example, the light valve can beso constructed that light 234 emitted perpendicularly to the fluorescentplane 231 is almost transmitted without any loss by the interferencefilm 232, but light 235 emitted by the fluorescent plane 231 in acertain direction forming an angle θ with the direction perpendicular tothe surface thereof is reflected by the interference film 232.

FIG. 17B shows the relation between the angle θ and the light amounttransmitted via the interference film 232 at this time. Light emittedover a wide angular region is transformed by the interference film 232into light spread only over a narrow angular region. Consequently lightis income into each of the liquid crystal light valves 201, 204 and 207.Thus it is possible to suppress the loss to the minimum and to obtain acolor image having a high brightness. Therefore, according to thepresent embodiment, it is possible to realize a satisfactorily long lifeby using cathode ray tubes as light sources. Further, since differentcathode ray tubes independent from each other are used for differentcolors, the optical system for separating the light from the source intodifferent colors becomes unnecessary and thus down sizing of the opticalsystem can be realized.

Furthermore, according to the present embodiment since emissionintensity for different colors can be controlled independently from eachother by controlling electron beam current for each of the CRTs 202, 205and 208, it is possible to effect color adjustment extremely easily.

Besides, although dispersed-type liquid crystal light valves are used inthe present embodiment, twisted-nematic-type liquid crystal light valvesor supertwisted-nematic-type liquid crystal light valve can be used aswell instead thereof. Further the shown positional relation between thedifferent colors is only an example and it can be modified arbitrarily.It is a matter of cause that it is possible to combine light by using acombination of dichroic mirrors instead of a dichroic prism, too.

Next the circuit construction of the control system 213 will beexplained, referring to FIG. 18.

An image signal 314 received from broadcast electromagnetic wave orinputted from a video deck, a video disk or another arbitrary signalsource is at first supplied to a color demodulating circuit 315 to beconverted there into different color signals of red, green and blue,which correspond to the three primary colors. The color signals obtainedby this conversion are stored in frame memories 317, 318 and 319 forevery frame in the form of digital data, respectively. Further, theimage signal 314 is also inputted to a sync signal separating circuit316 by which a reference sync signal component for the different signalsis separated therefrom, and a sync signal is generated by a sync signalreproducing circuit 320.

Red image signal data is inputted from a frame memory 317 controlled bythe reproducing circuit 320 to a signal circuit 323 for controlling theliquid crystal light valve for red 201. The light valve 201 iscontrolled there by the signal circuit 323 and a scanning circuit 324 toreproduce a red image. Further the sync signal generated by thereproducing circuit 320 is converted into horizontal and verticalscanning signals by a synchronization control circuit 321 and inaddition supplied to a CRT for red 202 disposed, adjacent to the lightvalve 201, through a beam control circuit 322 to control light emissionin a raster form in synchronism with reproduction of the red image fromthe liquid crystal light valve 201 so as to drive it as a red planelight source. In the same way, the liquid crystal light valves 204 and207 for green and blue are controlled by signal circuits 327 and 325 aswell as scanning circuits 328 and 326 to reproduce a green image and ablue image and at the same time light emission by CRTs 205 and 208 forgreen and blue is controlled in synchronism with reproduction of thegreen image and the blue image from the liquid crystal light valves 204and 207 for green and blue, respectively.

Consequently the three liquid crystal light valves 201, 204 and 207reproducing the different color images independently from each other,corresponding to the three primary colors, and the three CRTs 202, 205and 208 emitting light of different colors corresponding to the threeprimary colors are synchronously controlled by this control system 213,respectively, to reproduce a color image on the screen 212.

Light emission by each of the CRTs 202, 205 and 208 in the presentembodiment is effected by scanning the fluorescent plane in a rasterscan form with an electron beam. Consequently a light emitting point onthe CRT corresponding to a pixel on each of the liquid crystal lightvalves 201, 204 and 207 emits light only once during one frame. On theother hand, a liquid crystal light valve using TFTs is scanned by theline sequential scanning method and pixel information is held, until itis selected to be updated. Consequently, in an image reproducingapparatus using usual CRTs, a light emitting portion on the fluorescentplane thereof represents image information itself. On the contrary, theCRTs used in the present embodiment are used only as light sources.Increase in the total brightness is realized by increasing the currentintensity of the electron beam to increase the area emitting light forevery scanning and this will be explained around the light emittingstate of the CRT, referring to FIGS. 19A to 19D.

FIG. 19A enlargingly shows a part of the pixels of the liquid crystallight valve. The electron beam of the CRT corresponding thereto is sweptfrom the left to the right and downward in the order of a, b and c. Thepixel pitch P is about, e.g., 64 μm for a liquid crystal light valvehaving a size of 2 in. measured along a diagonal. The current intensityof the electron beam of the CRT is increased so that the diameter of theelectron beam is about 120 μm, which is twice as large as the pixelpitch. In this way, when the diameter of the electron beam is increasedwith respect to the size of a pixel in the corresponding liquid crystallight valve, the light emitting portion on the fluorescent plane of theCRT is enlarged so that pixels on a plurality of lines are irradiatedsimultaneously at each instant.

Now, when a pixel, which is hatched in the FIG. 19A, is considered,there is only one scanning signal selecting this pixel for every frame,as shown in FIG. 19B. The transmissivity at this pixel is held, until anew selecting signal is next applied thereto, as shown in FIG. 19C. Onthe other hand, the CRT is scanned downward in the order of a, b and cand the light emitting portion is moved in this direction. As theresult, the light emitting portion passes through the hatched pixelsuccessively three times so that the amount of transmitted light isincreased by a factor of about 2 with respect to that obtained when itis scanned separately in the direction a, b and c. Consequently,according to the present embodiment an extremely bright display image iseasily obtained and it is possible to realize the projection-type colordisplay apparatus having a small size, a high brightness and a longlife.

Such a liquid crystal light valve by the TFT driving method isfabricated at a relatively high cost because of a low yield at present.Therefore a modified example of the second embodiment, by which thenumber of used liquid crystal light valves is reduced so that increasein the cost is suppressed and that further down sizing is made possible,will be explained below.

FIG. 20 shows the construction of the present modified example. Theliquid crystal light valve used in the second embodiment describedpreviously is disposed before none of the CRTs, but a single liquidcrystal light valve is disposed between the dichroic prism 210 and theprojection lens 211. The constituent parts identical to those in thesecond embodiment are denoted by same reference numerals and explanationthereof will be omitted.

Red light 203 and blue light 209 produced by the CRTs for red and blue202 and 208 are reflected by reflecting films for red and blue 210a and210b and green light 206 produced by the CRT for green 205 passesthrough the dichroic prism 210. Light from the prism 210 is income intothe projection lens 211 after having been intensity-modulated by theliquid crystal light valve 401. Light of the three primary colorsemitted by the three CRTs 202, 205 and 208 is intensity-modulated by thesingle liquid crystal light valve 401 so as to display a color image onthe screen by means of the projection lens 211.

In the present modified example, the dichroic prism 210 is locatedbetween the different CRTs 202, 205 and 208 and the liquid crystal lightvalve 401. Therefore it is important that the light produced by thedifferent CRTs is income into the projection lens with a highefficiency. Also in the present modified example an interference film isstuck or laminated on the tube surface of each of the CRTs so that lightemitted by each of the CRTs comes into the projection lens with a highefficiency, as explained referring to FIG. 15.

Also in the present modified example, the three CRTs 202, 205 and 208 aswell as the liquid crystal light valve 401 are controlled by a controlsystem 213'. This control system 213' will be explained, referring toFIG. 21.

An image signal 314 received from broadcast electromagnetic wave, orinputted from a video deck, a video disk or another arbitrary signalsource is supplied at first to a color demodulating circuit 315 to beconverted there into different color signals of red, green and blue,which are the three primary colors. The color signals obtained by thisconversion are stored in frame memories 317, 318 and 319 for every framein the form of digital data, respectively. Further the image signal 314is also inputted to a separating circuit 316, by which a reference syncsignal component for the different signals is separated therefrom and async signal is reproduced by a reproducing circuit 357.

The frequency of the sync signal generated by the reproducing circuit357 is so determined to be three times as high as that of the syncsignal of the image signal 314.

From the first to the third frame, red, green and blue image signal dataare inputted from frame memories .317, 318 and 319 respectively,controlled by the reproducing circuit 357, to the signal circuit 360controlling the liquid crystal light valve 401. The liquid crystal lightvalve 401 is controlled by the signal circuit 360 and the scanningcircuit 361 to reproduce red, green and blue images.

Further, at the same time the sync signal generated by the reproducingcircuit 357 is converted into horizontal and vertical scanning signalsby a synchronization control circuit 358 and in addition supplied to theCRTs 202, 205 and 208 so as to control these CRTs in synchronism withreproduction of a red, a green and a blue image on the liquid crystallight valve 401.

Next states, where the single liquid crystal light valve 401 reproducingthe different color images corresponding to the three primary colors andthe three CRTs 202, 205 and 208 emitting light of different colorscorresponding similarly to the three primary colors are controlled insynchronism with each other as a result of the control by this controlsystem 213', will be explained, referring to FIGS. 22A to 22D.

FIGS. 22A to 22D show the reproduced image on the liquid crystal lightvalve 401, the fluorescent state of the CRT for red 202, the fluorescentstate of the CRT for green 205 and the fluorescent state of the CRT forblue 208, respectively, arranged time-sequentially, as shown downward by1 to 6. After 6 the process returns to 1. Consequently, in the presentmodified example, the color reproduction by a so-called "framesequential method", by which the images of different colors of red,green and blue are displayed time-sequentially during one frame period.

1 At first parts of a red image are reproduced successively on theliquid crystal light valve 401, starting from the highest line. Redlight is emitted successively, starting from the highest line of the CRTfor red 202, in synchronism with the state of the reproduction of thered image on the liquid crystal light valve 401 to display the redimage. At this time the lines on the CRTs for green and blue 205 and208, corresponding to the line emitting light on the CRT for red 202,emit no light.

2 On the liquid crystal light valve 401 the reproduction of the redimage is continued towards the lower lines and finally the red image isreproduced on the whole surface.

3 Then on the upper lines of the liquid crystal light valve 401, thereproduction of the green image begins and green light is emittedsuccessively by the lines on the CRT for green 205, starting from thehighest line, in synchronism with the state of the reproduction of thegreen image on the liquid crystal light valve 401.

4 Thereafter the CRT for green emits light on the whole surface so thatthe green image is reproduced on the whole surface of the liquid crystallight valve 401.

5 Next on the upper lines of the liquid crystal light valve 401, thereproduction of the blue image begins and blue light is emittedsuccessively by the lines on the CRT for blue 208, starting from thehighest line, in synchronism with the state of the reproduction of theblue image on the liquid crystal light valve 401.

6 Thereafter the blue image is reproduced on the whole surface of theliquid crystal light valve 401 and thus the image of one frame isdisplayed by the frame sequential reproduction of RGB. In the succeedingstate, the process returns to 1.

Consequently, according to the present modified example, the singleliquid crystal light valve 401 reproducing or generating the images ofdifferent colors corresponding to the three primary colors by the framesequential method and the three CRTs 202, 205 and 208 emitting thedifferent colors corresponding to the three primary colors arecontrolled successively in synchronism with each other so that the colorimage is projected on the screen 212 and that an enlarged image isreproduced.

Next the relation between variations in the transmissivity at the eachof the pixels of the liquid crystal panel and the light emitting stateof the CRTs in the present modified example will be explained, referringto FIGS. 23A to 23E.

FIG. 23A shows one frame period of a usual image signal. One frameperiod of the scanning signal applied to the liquid crystal light valve401 is 1/90 sec, which is equal to 1/3 of one frame period (1/30 sec) ofa usual image signal (e.g., video signal).

For the first frame the image signal of a red image is applied to thisliquid crystal light valve 401. Next a green image signal and then ablue image signal are applied thereto. The transmissivity of a certainpixel on the liquid crystal light valve 401 varies, depending on theimage signal applied thereto. That is, as shown by FIG. 23B, forexample, the transmissivity has a value corresponding to the red imageby the red image signal for the first frame, a value corresponding tothe green image by the green image signal for the second frame, and avalue corresponding to the blue image by the blue image signal. Further,although it is not shown in the figure, for the succeeding frame thetransmissivity has a value corresponding again to the red image of thesucceeding image.

On the other hand, for the first frame, the CRT for red 202 is scannedwith the electron beam in synchronism with the red image signal suppliedto the liquid crystal light valve 401 to emit light as shown in FIG.23C. Thereafter for the second frame, the CRT for green 205 is scannedwith the electron beam in synchronism with the green image signalapplied to the liquid crystal light valve 401 to emit light as shown inFIG. 23D. In the same way, for the third frame, the CRT for blue 208 isscanned with the electron beam in synchronism with the blue image signalapplied to the liquid crystal light valve 401 to emit light as shown inFIG. 23E. Consequently, according to the present modified example, oneliquid crystal light valve is sufficient and it is possible to realize aprojection-type color display apparatus having a smaller size at a lowcost.

Although, in the above explanation, the interference films 301, 302 and303 are disposed on the tube surfaces of the different CRTs,respectively, in order to income light emitted by the fluorescent planesof the CRT into the liquid crystal light valve with a high efficiency,another modified example for preventing this light loss will beexplained, referring to FIG. 24. FIG. 24 shows a cross-sectionalconstruction of the tube surface of each of the CRTs, in which a lenssurface 512 is formed on the tube surface of the CRT, which is oppositeto the fluorescent plane 231. Light 434 emitted by irradiating theelectron beam 233 into the fluorescent plane 231 is not dispersed owingto this lens surface 512, as shown in the figure. Thus the light canreach the liquid crystal light valve with a high efficiency and it isutilized sufficiently. This lens surface 512 forms a so-calledlenticular lens, in which a plurality of small lenses are arranged in anarray shape, and the focal point of each of the lenses is located so asto be in accordance with the fluorescent plane 231 described previously.This lens surface 512 may be formed either by processing the tubesurface 230 in a lens shape or by fabricating a separate lens array in asheet shape, which is pasted or stuck on the tube surface 230. Accordingto this modified example, the processing cost can be low and thus it ispossible to obtain a lower cost projection-type display apparatus.

What is claimed is:
 1. A projection type display apparatuscomprising:optical signal generating means including liquid crystalpanels of a reflective type corresponding to different spectra, eachliquid crystal panel including a plurality of pixels, and beingresponsive to electric signals inputted thereto, for selectivelyreflecting incident light components having the different spectra andincident thereto in units of pixels to generate optical signals havingthe different spectra, respectively; wherein each of the said liquidcrystal panels comprises:a monocrystalline semiconductor substrate witha transistor provided for each pixel on a surface thereof, thetransistor changing its conductive state in response to thecorresponding electric signal, and with a metal pixel electrode providedfor each pixel above the transistor and connected to the transistor, forselectively reflecting the corresponding light component in accordancewith the change in the conductive state of the transistor; a liquidcrystal layer including liquid crystal material of a light scatteringtype, the liquid crystal material scattering a light upon nonapplicationof a voltage and being transparent upon application of a voltage; and atransparent substrate with transparent counter electrodes providedthereon, the liquid crystal layer being sandwiched by the pixelelectrodes and the counter electrodes, the counter electrodesfunctioning to selectively apply the voltage to the liquid crystalmaterial together with the pixel electrodes in accordance with a changein the conductive state of the transistors; light supplying means forsupplying a light; an optical separating/combining system for separatingthe liquid from said light supplying means into the light components inaccordance with the spectra to irradiate the light components to theliquid crystal panels and for combining the optical signals to obtain anoptical image signal; and projecting means for focusing the opticalimage signal to project an enlarged image on a screen.
 2. A displayapparatus according to claim 1 wherein said liquid crystal layerincludes the liquid crystal material dispersed in a transparent organicmaterial.
 3. A display apparatus according to claim 2, wherein saidliquid crystal layer includes encapsulated nematic liquid crystaldispersed in a polymer.
 4. A display apparatus according to claim 1,wherein said liquid crystal layer includes smectic A phase liquidcrystal.
 5. A display apparatus according to claim 1, wherein saidoptical separating/combining system comprises a dichroic prism assemblyfor separating the parallel light from said light supplying means intothree light components in accordance with the spectra such that one ofthe light components travels in a straight path, another of the lightcomponents is reflected in a direction perpendicular to a direction ofthe light and the remaining light component is reflected in a directionopposite to the direction of the another light component, to irradiatethe light components to said liquid crystal panels, and for combiningthe optical signals generated by said liquid crystal panels into theoptical image signal.
 6. A display apparatus according to claim 5,further comprising a half mirror for reflecting a part of the light fromsaid light supplying means and for supplying the reflected part to saidoptical signal generating means and for transmitting a part of theoptical image signal to supply the transmitted part to said projectingmeans, and optical path of incident light from said half mirror to saidoptical signal generating means being the same as an optical path of theoptical image signal from said optical separating/combining system tosaid half mirror.
 7. A display apparatus according to claim 1, whereinsaid semiconductor substrate in each of said liquid crystal panelsfurther comprises a circuit for driving said transistors in response tothe corresponding electric signal.
 8. A display apparatus according toclaim 7, wherein said circuit of said semiconductor substrate in each ofsaid liquid crystal panels includes:a driving circuit for generating rowsignals to selectively drive each of rows of matrix-like pixels of eachof said liquid crystal panels; a supply circuit for selectivelygenerating column signals to drive each of columns of the pixels inresponse to the corresponding electric signal inputted thereto; and asample hold circuit disposed for each of the pixels for sampling inholding the corresponding column signal from said supply circuit inresponse to the corresponding row signal from said driving circuit.
 9. Adisplay apparatus according to claim 7, wherein said circuit includes:amatrix driving circuit for driving the pixels disposed in a matrix formin each of said liquid crystal panels; a frame memory for storingdisplay information for one image; and a control circuit for controllingsaid matrix driving circuit in accordance with the display informationstored in said frame memory.
 10. A display apparatus according to claim5, wherein said dichroic prism assembly is electrically connected witheach of said liquid crystal panels through solder bumps and with anexternal circuit by a flexible flat cable.
 11. A display apparatusaccording to claim 5, wherein an optical path of the light incident fromsaid light supplying means is different from an optical path of theoptical image signal.
 12. A projection-type display apparatuscomprising:optical signal generating means including a plurality ofliquid crystal panels respectively responsive to a plurality of electricsignals inputted thereto, for generating a plurality of optical signalshaving different spectra corresponding to said plurality of electricsignals; wherein each of said liquid crystal panels comprises:asemiconductor structure, which includes a semiconductor layer having atransistor for each of a plurality of pixels, for driving said eachliquid crystal panel in units of pixels in response to corresponding oneof said electric signals, and a pixel electrode layer having a pixelelectrode for each pixel connected to the corresponding transistor, forselectively reflecting a light incident to said each liquid crystalpanel in units of pixels as one of said optical signals; a glassstructure including a transparent glass substrate and a transparentelectrode layer formed on a surface of said glass substrate facing saidsemiconductor structure, an axis perpendicular to a surface of saidglass substrate opposite to said transparent electrode layer being notcoincident with an optical axis of the incident light; and alight-scattering-type liquid crystal layer interposed between saidsemiconductor structure and said glass structure; control meansresponsive to an inputted electric image signal representing an image,for generating the plurality of electric signals to output the generatedelectric signals to said optical signal generating means and forcontrolling said optical signal generating means; a combining opticalsystem for visually combining the plurality of optical signals to obtainan optical image signal so as to provide said image; and projectingmeans for focusing said optical image signal to project an enlargedimage of said image on a screen.
 13. A projection type display apparatuscomprising:optical signal generating means including a plurality ofliquid crystal panels respectively responsive to a plurality of electricsignals inputted thereto, for generating a plurality of optical signalshaving different spectra corresponding to said plurality of electricsignals; control means responsive to an inputted electric image signalrepresenting an image, for generating the plurality of electric signalsto output the generated electric signals to said optical signalgenerating means and for controlling said optical signal generatingmeans; means including a light source, for supplying light emitted fromsaid light source as substantially parallel light; aseparating/combining optical system for separating the parallel light inaccordance with the spectra to supply the separated parallel light tosaid liquid crystal panels, respective and for visually combining theplurality of optical signals to obtain an optical image signal so as toprovide said image, wherein said optical signal generating meansreflects the parallel light in accordance with the electric signals togenerate the optical signals; projecting means including a lens, forfocusing said optical image signal by use of the lens to project anenlarged image of said image on a screen; a photodetector for detectinga light amount; and photodetector driving means for moving saidphotodetector to a focal point of said lens in replacing said lightsource such that a position of said light source can be adjusted basedon a detecting result by said photodetector.
 14. A display apparatusaccording to claim 13, further comprising:light source driving means formoving said light source; and adjusting means for previously storing anoptimum light amount range for every kind of lamps used as said lightsource and for driving said light source driving means in accordancewith the stored optimum light amount range and the detected light amountby said photodetector such is in said optimum light amount range for thekind of lamp used as said light source.
 15. A projection type displayapparatus comprising:light emitting means including a light source, foremitting a light; a half mirror for transmitting about one-half of thelight incident from said light emitting means to said half mirror andreflecting a remaining half; an optical separating/combining system forseparating the transmitted light and the reflected light from said halfmirror into transmitted light components having different spectra andreflected light components having different spectra, and synthesizing aneven scanning line optical image signal from even scanning line lightsignals and an odd scanning line image signal from odd scanning linelight signals and synthesizing an optical image signal from the even andodd scanning line image signals to supply the optical image signal tosaid half mirror; optical signal generating means including two sets ofliquid crystal panels for even and odd scanning lines, each of saidliquid crystal panels being provided for one of the reflected andtransmitted light components and being of a light scattering type, andresponsive to electric signals inputted thereto, for generating the evenand odd scanning light signals to output the generated even and oddscanning light signals to said separating/combining system,respectively; control means responsive to an inputted electric imagesignal representing an image, for generating the electric signals tosupply each electric signal to one of said liquid crystal panels; andprojecting means for focusing the optical image signal transmitted bysaid half mirror to project an optical image of said image on a screen.16. A method for projecting an enlarged image on a screen comprising thesteps of:separating an electric image signal representing the image intoa plurality of electric signals corresponding to different spectra;separating an incident light into three light components correspondingto primary colors by a dichroic prism assembly, a path of the lightcomponent transmitted by said prism assembly being perpendicular to eachof the remaining light components; selectively reflecting thecorresponding light component in units of pixels in response to thecorresponding electric signal by a corresponding liquid crystal panelwhich includes liquid crystal material of a light scattering type and apixel electrode for each pixel such that the corresponding lightcomponent is scattered in each pixel upon non-application of a voltageto the pixel and such that the corresponding light component isreflected by the pixel electrode of each pixel upon application of avoltage to the pixel and generating optical signals corresponding to theelectric signals; synthesizing an optical image signal from the opticalsignals by the dichroic prism assembly; and enlarging and projecting theoptical image signal on a screen.
 17. A method according to claim 16,wherein said step of projecting the optical image signal comprises thesteps of:collecting the optical image signal by a first lens; andprojecting the image corresponding to the optical image signalscollected by said first lens on the screen by a second lens, an opticalaxis of the incident light being different from that of the opticalimage signal.
 18. A projection type display apparatus comprising:opticalsignal generating means including liquid crystal panels of a reflectivetype corresponding to different spectra, each liquid crystal displaypanel including a plurality of pixels, and being responsive to electricsignals inputted thereto, for selectively reflecting incident lightcomponents having the different spectra and incident thereto in units ofpixels to generate optical signals having the different spectra,respectively; wherein each of said liquid crystal panels comprises:asemiconductor substrate with a transistor provided for each pixel on asurface thereof, the transistor changing its conductive state inresponse to the corresponding electric signal, and with a pixelelectrode provided for each pixel above the transistor and connected tothe transistor, for selectively reflecting the corresponding lightcomponent in accordance with the change in the conductive state of thetransistor; a liquid crystal layer including liquid crystal materialchanging its scattering state and transparent state in accordance with avoltage applied thereto; a transparent substrate with transparentcounter electrodes provided thereon, the liquid crystal layer beingsandwiched by the pixel electrodes and the counter electrodes, thecounter electrodes functioning to selectively apply the voltage to theliquid crystal material together with the pixel electrodes in accordancewith a change in the conductive state of the transistors; lightsupplying means for supplying a light; an optical separating/combiningsystem for separating the light from said light supplying means into thelight components in accordance with the spectra to irradiate the lightcomponents to the liquid crystal panels and for combining the lightcomponents reflected from said liquid crystal panels to obtain anoptical image signal; and projecting means for focusing the opticalimage signal to project an enlarged image on a screen.
 19. A displayapparatus according to claim 18, further comprising control meansresponsive to an inputted electric image signal representing an image,for generating the plurality of electric signals to output the generatedelectric signals to said optical signal generating means and forcontrolling said optical signal generating means.
 20. A displayapparatus according to claim 18, wherein said light supplying meanscomprises a light source for supplying light emitted from said lightsource as substantially parallel light.
 21. A display apparatusaccording to claim 20, further comprising positioning means forpositioning said light source in order to correct deviation of anoptical axis between said light source and said projecting means.
 22. Adisplay apparatus according to claim 21, wherein said positioning meanscomprises a photodetector for detecting a light amount, andphotodetector driving means for moving said photodetector to a focalpoint of a lens of said projecting means such that a position of saidlight source is adjustable in accordance with a detecting result of saidphotodetector.